THE REPTILIAN CLASS OP THE MOSASAURIDJE. 



709 



coalesced neural arch represents at last the entire vertebra. All 

 these modifications, shown in the plates of Cuvier and Goldfuss, are 

 repeated in the figures of the vertebrae of Mosasaurians in plates 

 xviii., xix., xx., xxi., xxiii., xxiv., xxvi., xxvii., xxix., xxx., xxxiv., 

 and xxxv. of Prof. Cope's great work ; in every figure the zygosphene 

 and zygantrum are absent. 



In most of these characters the Mosasaurians retain the type of 

 the Lacertian vertebras, and especially of the existing marine kinds. 

 Where the Mosasaurian vertebras depart from that type, the charac- 

 ters are peculiar to the extinct group. In no genus are Ophidian 

 modifications manifested. In the speedy loss of the zygapophyses 

 there is a Cetacean analogy ; but it is adaptive, in relation to the 

 locomotion of the great Sea-lizard. 



A few words on a character which Prof. Cope assigns to his genus 

 Clidastes, viz. : — " the vertebras united by the zygosphenal as well 

 as the usual articulation ; the zygosphene elevated but little above 

 the plane of the zygapophyses "*. 



In the plates xviii. and xxiii. given to the vertebras of the species 

 stenops and planifrons, the parts and processes are, as usual, not 

 indicated. In plate xiii. of the ' Monograph of the Fossil Reptilia 

 of the London Clay' (Palasontographical volume for 1850), the 

 zygosphene in Python and Iguana is marked zs, and the zygan- 

 trum za. 



I subjoin a figure (fig. 23) of, apparently, the best-preserved vertebra 



Fig. 22. 



Fig. 23. 



ns 



Fig. 24. 



Iguana 



Python. 



of Clidastes stenops (Cope, pi. xviii. fig. 4a), and corresponding figures 



* Op. cit. p. 130. If Prof. Cope could spare me, out of his abundance of 

 pythonomorphous vertebra, one which has the zygosphene and zygantrum, I 

 will, with pleasure, acknowledge and figure the structure, and give such vertebra 

 a prominent position in our Mosasaurian cabinet. 



Q.J.G.S. No. 132. 3 a 



